Promise的串行调用 about front-end-interview HOT 2 OPEN

let arr = [
()=>{ 
     return new Promise(res=>{ 
          console.log("run1", Date.now());
          res()
     }) 
}, 
()=>{ 
     return new Promise(res=>{ 
          console.log("run2", Date.now());
          res()
     }) 
}, 
()=>{ 
     return new Promise(res=>{ 
          console.log("run3", Date.now());
          res()
     }) 
}, 
]